Characteristic frequency of the main component of the broad-band noise as a function of X-ray luminosity. Open circles represent the DB (supercritical regime), filled circles the HB (subcritical regime). In XTE J0658–073, orange circles correspond to the flares. In Swift J1656.6–5156, open circles (in orange) and open squares give the frequency of L₁ with and without the L₂ component, respectively. We assume L_Edd = 1.7 × 10³⁸ erg s^-1.